GaSb Epitaxial Layers Research Articles

Легированный кремнием GaSb, выращенный методом ГФЭМОС в широком диапазоне соотношений V/III

Charachterization of Si-doped GaSb epitaxial layers grown by metal organic vapor phase epitaxy is presented. Samples are grown at constant SiH4 flow with a TMSb/TEGa ratio ranged from 1 to 50. X-ray diffraction, Raman scattering, photoluminescence, resistivity, free carrier concentration and their mobility are studied.

Higher electrical activation of ion-implanted Si over S in GaSb epitaxial layers

Ion implantation of the amphoteric dopant Si compared to the natural n-type dopant S in GaSb epitaxial films results in a higher dopant activation with better surface morphology and crystallinity. GaSb films were grown by molecular beam epitaxy (MBE) on semi-insulating GaAs (001) substrates. Ion implantation for both ions was carried out at an energy of 50 keV and a fluence of 1 × 1015 ions/cm2. Raman spectroscopy revealed a better crystallinity as well as a lower Sb out-diffusion for Si implantation as compared to S after annealing. Van der Pauw Hall measurements confirm the donor nature of the amphoteric dopant Si and with a dopant activation that is 3 times higher than the natural donor S. The electrical activation for both implants increases significantly after thermal annealing. Using temperature (20 K–300 K) vs conductivity measurement and displacement per atom (dpa) estimation, implantation-induced defect-related conduction mechanism is discussed. The results suggest the scope of Si as a viable n-type dopant in GaSb.

High-Resistivity Gallium Antimonide Produced by Metal–Organic Vapor-Phase Epitaxy

The results of studies of nominally undoped epitaxial p-GaSb layers grown by metal–organic vapor-phase epitaxy at a ratio TMSb/TEGa in the range from 1 to 50 are reported. At the ratio TMSb/TEGa = 50, GaSb epitaxial layers, whose resistivity is 400 Ω cm, are produced. It is shown that, for such layers, the crystal quality assessed by several methods remains comparable to the quality of n-GaSb substrates used for the growth of nominally undoped GaSb layers.

Mid-Infrared InAs/InAsSb Superlattice nBn Photodetector Monolithically Integrated onto Silicon

Mid-infrared (MIR) silicon photonics holds the potential for realizing next generation ultracompact spectroscopic systems for applications in gas sensing, defense, and medical diagnostics. The direct epitaxial growth of antimonide-based compound semiconductors on silicon provides a promising approach for extending the wavelength of silicon photonics to the longer infrared range. This paper reports on the fabrication of a high performance MIR photodetector directly grown onto silicon by molecular beam epitaxy. The device exhibited an extended cutoff wavelength at ∼5.5 μm and a dark current density of 1.4 × 10–2 A/cm2 under 100 mV reverse bias at 200 K. A responsivity of 0.88 A/W and a specific detectivity in the order of 1.5 × 1010 Jones was measured at 200 K under 100 mV reverse bias operation. These results were achieved through the development of an innovative structure which incorporates a type-II InAs/InAsSb superlattice-based barrier nBn photodetector grown on a GaSb-on-silicon buffer layer. The difficulties in growing GaSb directly on silicon were overcome using a novel growth procedure consisting of an efficient AlSb interfacial misfit array, a two-step growth temperature procedure and dislocation filters resulting in a low defect density, antiphase domain free GaSb epitaxial layer on silicon. This work demonstrates that complex superlattice-based MIR photodetectors can be directly integrated onto a Si platform, which provides a pathway toward the realization of new, high performance, large area focal plane arrays and mid-infrared integrated photonic circuits.

Swift heavy silver (Ag+7) ion irradiation induced self assembled nanodots on MBE grown Gallium antimonide (GaSb)

100 MeV swift heavy silver (Ag+7) ion irradiation at normal incidence results in the formation of dense and ordered nanosized dots on molecular beam epitaxy (MBE) grown GaSb epitaxial layers. The shape, size and density of the nanodots are found to be strongly dependent on the ion fluence. Ripening of the dots with change in shape from cone to dome, and finally smoothening of the surface is observed with increasing ion fluence. The dot formation mechanism is explained on the basis of a surface instability introduced by combination of sputtering, step or kink Ehrlich-Schwoebel barrier effect and surface diffusion of mobile adatoms. Raman spectroscopy and high resolution X-ray diffraction results suggest preservation of crystallinity in the irradiated epilayers with presence of small tensile stress. Prevention of amorphisation in the irradiated samples is explained on the basis of a dynamic self annealing process during irradiation.

InAs0.9Sb0.1-based hetero-p-i-n structure grown on GaSb with high mid-infrared photodetection performance at room temperature

We present the design, fabrication, and characterization of middle-wavelength infrared photodetector based on active InAs0.9Sb0.1-based hetero-p-i-n structure grown on GaSb substrate. In this structure, the active absorption layer is sandwiched between thin quaternary p-type and n-type AlInAsSb layers and a heavily doped AlGaSb layer is introduced to reduce dark current. We observed good lattice matching between GaSb substrates and epitaxial layers by high-resolution X-ray diffraction. Photoluminescence (PL) spectrum at 13 K shows a full width at half maximum of ~ 29 meV, demonstrating good quality active absorption layers. The band gap energy of InAs0.9Sb0.1 is derived as ~ 0.322 eV at 0 K by Varshni fitting from PL spectra at different temperatures. A rather flat room-temperature responsivity of ~ 0.8–0.9 AW−1 over a wavelength range of ~ 2.1 µm is demonstrated without antireflection coating. A detectivity of 8.9 × 108 cm Hz1/2 W−1 at 3.5 µm for room-temperature operation is achieved under applied bias of − 0.5 V.

Anti phase boundary free GaSb layer grown on 300 mm (001)-Si substrate by metal organic chemical vapor deposition

Antiphase boundaries free GaSb epitaxial layers with low surface roughness (<0.5nm) have been synthesized on standard microelectronic 300mm nominal (001)-Si substrates by metal organic chemical vapor deposition using a two-step growth process. By adjusting the growth temperature and the thickness of the nucleation layer, antiphase boundary free GaSb layers as thin as 250nm are obtained. The 12% lattice mismatch between GaSb and Si is accommodated by both the formation of threading dislocations and a periodic array of 90° misfit dislocations at the interface. A GaSb layer inserted between AlSb barriers has been grown on an optimized GaSb/(001)-Si buffer layer and exhibits room temperature photoluminescence.

Demonstrating antiphase domain boundary-free GaAs buffer layer on zero off-cut Si (0 0 1) substrate for interfacial misfit dislocation GaSb film by metalorganic chemical vapor deposition

High quality 40 nm GaSb thin film was grown on the zero off-cut Si (0 0 1)-oriented substrate using metalorganic chemical vapor deposition with the temperature-graded GaAs buffer layer. The growth time of the GaAs nucleation layer, which was deposited at a low temperature of 490 °C, is systematically investigated in this paper. Cross-sections of the high resolution transmission electron microscopy images indicate that the GaAs compound formed 3D-islands first before to quasi-2D islands, and finally formed uniform GaAs layer. The optimum thickness of the 490 °C-GaAs layer was found to be 10 nm to suppress the formation of antiphase domain boundaries (APDs). The thin GaAs nucleation layer had a root-mean-square surface roughness of 0.483 nm. This allows the continued high temperature GaAs buffer layer to be achieved with low threading dislocation density of around 7.1 × 106 cm−2 and almost invisible APDs. Finally, a fully relaxed GaSb film was grown on the top of the GaAs/Si heterostructure using interfacial misfit dislocation growth mode. These results indicate that the GaSb epitaxial layer can be grown on Si substrate with GaAs buffer layer for future p-channel metal-oxide-semiconductor field effect transistors (MOSFETs) applications.

Bandgap reduction of InP and GaSb epitaxial layers containing Bi

We report on the growth of InPBi and GaSbBi epitaxial layers by liquid phase epitaxy. Photoluminescence measurements showed a bandgap reduction of 55 meV for InPBi and 24 meV for GaSbBi due to the incorporation of Bi in the III-V lattice.

Magnetic field enhanced terahertz pulse emission from a femtosecond laser excited GaSb epitaxial layer

An undoped GaSb epitaxial layer has been grown on a GaAs substrate by molecular beam epitaxy. It has been found that GaSb could be a potential surface terahertz (THz) emitter photoexcited by 1.55 μm femtosecond laser pulses since the maximum optical-to-THz power conversion efficiency is at around this wavelength. The THz field strength is 10 dB weaker as compared with that generated from narrow-gap InAs at these energies of quanta. Furthermore, the samples were exposed to a constant magnetic field which enhances THz emission and allows signal registration in the line-of-sight geometry.

Growth of ultrathin GaSb layer on GaAs using metal–organic chemical vapor deposition with Sb interfacial treatment

GaSb epitaxial layers were directly grown on GaAs substrates by metal–organic chemical vapor deposition involving Sb interfacial treatment with optimized growth temperature and V/III ratio. The interfacial treatment effectively reduces the surface energy and strain energy difference, resulting in a quasi-2D growth mode. When the GaSb layer was grown at 520 °C, the strain induced by lattice mismatch was accommodated by 90° dislocations with a period of 5.67 nm. By optimizing the V/III ratio, the surface roughness of the ultrathin GaSb/GaAs heterostructure was reduced, resulting in a reduced carrier scattering and improved electronic properties.

Integration of atomic layer deposited high-k dielectrics on GaSb via hydrogen plasma exposure

In this letter we report the efficacy of a hydrogen plasma pretreatment for integrating atomic layer deposited (ALD) high-k dielectric stacks with device-quality p-type GaSb(001) epitaxial layers. Molecular beam eptiaxy-grown GaSb surfaces were subjected to a 30 minute H2/Ar plasma treatment and subsequently removed to air. High-k HfO2 and Al2O3/HfO2 bilayer insulating films were then deposited via ALD and samples were processed into standard metal-oxide-semiconductor (MOS) capacitors. The quality of the semiconductor/dielectric interface was probed by current-voltage and variable-frequency admittance measurements. Measurement results indicate that the H2-plamsa pretreatment leads to a low density of interface states nearly independent of the deposited dielectric material, suggesting that pre-deposition H2-plasma exposure, coupled with ALD of high-k dielectrics, may provide an effective means for achieving high-quality GaSb MOS structures for advanced Sb-based digital and analog electronics.

(Invited) InGaSb MOSFET Channel on Metamorphic Buffer: Materials, Interfaces and Process Options

High quality bulk GaSb and InGaSb quantum wells grown on GaAs substrates were MBE grown using a AlGaSb(As) metamorphic buffer layers to reduce dislocation density down to 107cm-2. Strained In0.36Ga0.64Sb quantum wells with a biaxial compressive strain of 1.8% showed the highest mobility of 1020 cm2/Vs and a low sheet resistance of 3.9 kΩ/sq. at hole sheet at hole density of 1.9x1012 cm-2. Buried channel design with an AlGaSb top barrier improved hole mobility by only 30% compared to surface QW channels. Improving the interface trap density down to 1012 cm-2eV-1 was realized using an amorphous Si layer (in-situ gate oxide) or an InAs layer (ex-situ gate) as a gate passivation. p++-GaSb epitaxial contact layers were developed and showed the leakage current of ~0.1 mA/cm2 not affected by growth defects. Critical elements of "gate-last" InGaSb MOSFET fabrication process were developed utilizing an InAs etch stop layer to avoid high temperature processing of the gate stack.

Causes and elimination of pyramidal defects in GaSb-based epitaxial layers

Here, the authors report on the occurrence, cause, and elimination of pyramidal defects in layers of GaSb grown by molecular beam epitaxy on GaSb substrates. These defects are typically 3–8 nm high, 1–3 μm in diameter, and shaped like pyramids. Their occurrence in the growth of GaSb buffer layers can propagate into subsequent layers such as GaSb, GaInAsSb, and GaSb/InAs superlattices. Defects are nucleated during the early stages of growth after the thermal desorption of native oxide from the GaSb substrate. These defects grow into pyramids due to a repulsive Ehrlich–Schwoebel potential on atomic step edges leading to an upward adatom current. The defects reduce in density with growth of GaSb. The insertion of a thin AlAsSb layer into the early stages of the GaSb buffer increases the rate of elimination of the defects, resulting in a smooth surface within 500 nm. The acceleration of defect reduction is due to the temporary interruption of step-flow growth induced by the AlAsSb layer. This leads to a reduced isolation of the pyramids from the GaSb epitaxial layer and allows the pyramidal defects to smooth out.

Strain relief and growth optimization of GaSb on GaP by molecular beam epitaxy

In this paper, the impact of growth parameters on the strain relaxation of highly lattice mismatched (11.8%) GaSb grown on GaP substrate by molecular beam epitaxy has been investigated. The surface morphology, misfit dislocation and strain relaxation of the GaSb islands are shown to be highly related to the initial surface treatment, growth rate and temperature. More specifically, Sb-rich surface treatment is shown to promote the formation of Lomer misfit dislocations. Analysis of the misfit dislocation and strain relaxation as functions of the growth temperature and rate led to an optimal growth window for a high quality GaSb epitaxial layer on (001) GaP. With this demonstrated optimized growth, a high mobility (25 500 cm2 V −1 s−1 at room temperature) AlSb/InAs heterostructure on a semi-insulating (001) GaP substrate has been achieved.

Optimization of growth parameters for MOVPE-grown GaSb and Ga1−xInxSb

The triethylgallium/trimethylantimony (TEGa/TMSb) precursor combination was used for the metal-organic vapour phase epitaxial growth of GaSb at a growth temperature of 520°C at atmospheric pressure. Trimethylindium was added in the case of Ga1−xInxSb growth. The effects of group V flux to group III flux ratio (V/III ratio) on the crystallinity and optical properties of GaSb layers are reported. It has been observed from the crystalline quality and optical properties that nominal V/III ratios of values greater than unity are required for GaSb epitaxial layers grown at this temperature. It has also been shown that Ga1−xInxSb can be grown using TEGa as a source of gallium species at atmospheric pressure. The relationship between Ga1−xInxSb vapour composition and solid composition has been studied at a V/III ratio of 0.78.

Investigation of electrical and optothermal properties of Si-doped GaSb epitaxial layers by the Hall effect, PL measurement and photothermal deflection spectroscopy

The aim of this work is to investigate the influence of Si-doping on the optical, thermal and electrical properties of GaSb epitaxial layers. Such an influence was quantified through photoluminescence (PL), mirage effect (photothermal spectroscopy) and Hall effect measurements. Several GaSb samples, grown by Molecular Beam Epitaxy (MBE) on (100)-oriented GaAs semiinsulating substrates, with different Si-doping levels ranging from 4.95×1016at .cm−3 up to 8.11.1019at.cm−3 were tested. As a comparison, the same measurements were also performed on a GaSb non intentionally doped layer. The Hall effect data shows a monotonic decrease in carrier mobility when the hole concentration increase.The effect of band-to-band, band-impurity transitions on the PL gap E0 and the influence of high impurity concentration on the PL and absorption spectra have been also studied. Finally, the optical absorption changes induced by Si-doping on GaSb samples were investigated by photothermal deflection. It was shown that this technique allows a very precise deduction of the real interband gap energy of a semiconductor material as GaSb.Thermal conductivities were also deduced from the photothermal deflection measurements. The found values are very low due to the thermal resistivity of the layer-substrate interface but also due to the lattice-mismatch between GaSb epilayers and the GaAs substrate. However, the contribution of the free carriers to the thermal conductivity, with a high p-doping level (p>1019cm−3), could be highlighted.

Rocking Curve Imaging Studies of Laterally Overgrown GaAs and GaSb Epitaxial Layers

X-ray rocking curve imaging technique was used to study crystallographic perfection of laterally overgrown epitaxial structures. We focus on rocking curve imaging studies of Si-doped GaAs and GaSb laterally overgrown layers grown by liquid phase epitaxy on SiO2 masked GaAs and GaSb/GaAs substrates, respectively. High spatial resolution offered by rocking curve imaging technique allows studying the effect of laterally overgrown epitaxial wing tilt towards the mask. Distribution of tilt magnitude over the area of laterally overgrown epitaxial stripes is easily determined. In heteroepitaxial GaSb/GaAs laterally overgrown epitaxial structures local mosaicity in the wing area was detected. Since individual grains are clearly visible on rocking curve imaging maps, their size and relative misorientation can be determined.

Structural Analysis of Highly Relaxed GaSb Grown on GaAs Substrates with Periodic Interfacial Array of 90° Misfit Dislocations

We report structural analysis of completely relaxed GaSb epitaxial layers deposited monolithically on GaAs substrates using interfacial misfit (IMF) array growth mode. Unlike the traditional tetragonal distortion approach, strain due to the lattice mismatch is spontaneously relieved at the heterointerface in this growth. The complete and instantaneous strain relief at the GaSb/GaAs interface is achieved by the formation of a two-dimensional Lomer dislocation network comprising of pure-edge (90°) dislocations along both [110] and [1-10]. In the present analysis, structural properties of GaSb deposited using both IMF and non-IMF growths are compared. Moiré fringe patterns along with X-ray diffraction measure the long-range uniformity and strain relaxation of the IMF samples. The proof for the existence of the IMF array and low threading dislocation density is provided with the help of transmission electron micrographs for the GaSb epitaxial layer. Our results indicate that the IMF-grown GaSb is completely (98.5%) relaxed with very low density of threading dislocations (105 cm−2), while GaSb deposited using non-IMF growth is compressively strained and has a higher average density of threading dislocations (>109 cm−2).

Photoluminescence properties of GaSb epitaxial layers passivated in hydrogen plasma

AbstractUndoped and Si‐doped GaSb layers grown by low pressure MOVPE have been treated in hydrogen plasma and the effect of this treatment on photoluminescent (PL) and electrical properties is presented. Hall‐effect and PL measurements reveal that hydrogenation leads to reduction in the concentration of electrically active native acceptors, while the concentration of shallow acceptor SiSb remain practically unaffected. The hydrogenation of layers grown at Sb rich conditions results in nearly complete quenching of the PL line peaking at 896.5 meV, denoted in the literature as BE4. The origin of the BE4 line is ascribed to radiative recombination of excitons bound to a “bare” gallium vacancy. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)